When the quality is thought as dynamic characteristic , the characteristic is also called "Functionality" in quality engineering.
"Dynamic characteristic" is used when mathematics is important. "Functionality" is used when thought for quality is important.
The quality we want to have is called "Expected Functionality". And the law to make the expected functionality is called "Basic Functionality".
Quality engineering tries to control functionality. Because it consider functionality has linearity and easy to control. (I do not believe this hypothesis.)
The example of functionality is the Ohm's law.
It is difficult to improve the quality if the quality is difficult to be measured.
The thought of "functionality" looks for the index that has linearity. Such index is easy to measure and difference of action is clearly found.
"Select indexes which is easy to measure" is a good approach. The thought, "functionality" itself has doubt but the thought indicates useful approach.
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